Control channel signaling using code points for indicating the scheduling mode

ABSTRACT

The invention relates to a control channel signal for use in a mobile communication system providing at least two different scheduling modes. Further the invention relates to a scheduling unit for generating the control channel signal and a base station comprising the scheduling unit. The invention also relates to the operation of a mobile station and a base station for implementing a scheduling mode using the control channel signal. In order to facilitate the use of different scheduling schemes for user data transmission while avoiding an additional flag for indicating the scheduling mode in the control signaling, the invention proposes the use of code points in existing control channel signal fields. Further, the invention proposes a specific scheduling mode for use in combination with the proposed control channel signal. According to this scheduling mode control channel information is only provided for retransmissions, while initial transmissions are decoded using blind detection.

FIELD OF THE INVENTION

The invention relates to a control channel signal for use in a mobilecommunication system providing at least two different scheduling modes.Further, the invention relates to a scheduling unit for generating thecontrol channel signal and a base station comprising the schedulingunit. The invention also relates to the operation of a mobile stationand a base station for implementing a scheduling mode using the controlchannel signal proposed by the invention.

TECHNICAL BACKGROUND

Packet-Scheduling and Shared Channel Transmission

In wireless communication systems employing packet-scheduling, at leastpart of the air-interface resources are assigned dynamically todifferent users (mobile stations—MS or user equipments—UE). Thosedynamically allocated resources are typically mapped to at least onePhysical Uplink or Downlink Shared CHannel (PUSCH or PDSCH). A PUSCH orPDSCH may for example have one of the following configurations:

One or multiple codes in a CDMA (Code Division Multiple Access) systemare dynamically shared between multiple MS.

One or multiple subcarriers (subbands) in an OFDMA (Orthogonal FrequencyDivision Multiple Access) system are dynamically shared between multipleMS.

Combinations of the above in an OFCDMA (Orthogonal Frequency CodeDivision Multiplex Access) or a MC-CDMA (Multi Carrier-Code DivisionMultiple Access) system are dynamically shared between multiple MS.

FIG. 1 shows a packet-scheduling system on a shared channel for systemswith a single shared data channel. A sub-frame (also referred to as atime slot) reflects the smallest interval at which the scheduler (e.g.,the Physical Layer or MAC Layer Scheduler) performs the dynamic resourceallocation (DRA). In FIG. 1, a TTI (transmission time interval) equal toone sub-frame is assumed. It should be born noted that generally a TTImay also span over multiple sub-frames.

Further, the smallest unit of radio resources (also referred to as aresource block or resource unit), which can be allocated in OFDMsystems, is typically defined by one sub-frame in time domain and by onesubcarrier/subband in the frequency domain. Similarly, in a CDMA systemthis smallest unit of radio resources is defined by a sub-frame in thetime domain and a code in the code domain.

In OFCDMA or MC-CDMA systems, this smallest unit is defined by onesub-frame in time domain, by one subcarrier/subband in the frequencydomain and one code in the code domain. Note that dynamic resourceallocation may be performed in time domain and in code/frequency domain.

The main benefits of packet-scheduling are the multi-user diversity gainby time domain scheduling (TDS) and dynamic user rate adaptation.

Assuming that the channel conditions of the users change over time dueto fast (and slow) fading, at a given time instant the scheduler canassign available resources (codes in case of CDMA, subcarriers/subbandsin case of OFDMA) to users having good channel conditions in time domainscheduling.

Specifics of DRA and Shared Channel Transmission in OFDMA

Additionally to exploiting multi-user diversity in time domain by TimeDomain Scheduling (TDS), in OFDMA multi-user diversity can also beexploited in frequency domain by Frequency Domain Scheduling (FDS). Thisis because the OFDM signal is in frequency domain constructed out ofmultiple narrowband subcarriers (typically grouped into subbands), whichcan be assigned dynamically to different users. By this, the frequencyselective channel properties due to multi-path propagation can beexploited to schedule users on frequencies (subcarriers/subbands) onwhich they have a good channel quality (multi-user diversity infrequency domain).

For practical reasons in an OFDMA system the bandwidth is divided intomultiple subbands, which consist out of multiple subcarriers. I.e., thesmallest unit on which a user may be allocated would have a bandwidth ofone subband and a duration of one slot or one sub-frame (which maycorrespond to one or multiple OFDM symbols), which is denoted as aresource block (RB). Typically, a subband consists of consecutivesubcarriers. However, in some case it is desired to form a subband outof distributed non-consecutive subcarriers. A scheduler may alsoallocate a user over multiple consecutive or non-consecutive subbandsand/or sub-frames.

For the 3GPP Long Term Evolution (3GPP TR 25.814: “Physical LayerAspects for Evolved UTRA”, Release 7, v. 7.1.0, October 2006 —availableat http://www.3gpp.org and incorporated herein by reference), a 10 MHzsystem (normal cyclic prefix) may consist out of 600 subcarriers with asubcarrier spacing of 15 kHz. The 600 subcarriers may then be groupedinto 50 subbands (a 12 adjacent subcarriers), each subband occupying abandwidth of 180 kHz. Assuming, that a slot has a duration of 0.5 ms, aresource block (RB) spans over 180 kHz and 0.5 ms according to thisexample.

In order to exploit multi-user diversity and to achieve scheduling gainin frequency domain, the data for a given user should be allocated onresource blocks on which the users have a good channel condition.Typically, those resource blocks are close to each other and therefore,this transmission mode is in also denoted as localized mode (LM).

An example for a localized mode channel structure is shown in FIG. 2. Inthis example neighboring resource blocks are assigned to four mobilestations (MS1 to MS4) in the time domain and frequency domain. Eachresource block consists of a portion for carrying Layer 1 and/or Layer 2control signaling (L1/L2 control signaling) and a portion carrying theuser data for the mobile stations.

Alternatively, the users may be allocated in a distributed mode (DM) asshown in FIG. 3. In this configuration, a user (mobile station) isallocated on multiple resource blocks, which are distributed over arange of resource blocks. In distributed mode a number of differentimplementation options are possible. In the example shown in FIG. 3, apair of users (MSs ½ and MSs ¾) shares the same resource blocks. Severalfurther possible exemplary implementation options may be found in 3GPPRAN WG#1 Tdoc. R1-062089, “Comparison between RB-level andSub-carrier-level Distributed Transmission for Shared Data Channel inE-UTRA Downlink”, August 2006 (available at http://www.3gpp.org andincorporated herein by reference).

It should be noted, that multiplexing of localized mode and distributedmode within a sub-frame is possible, where the amount of resources (RBs)allocated to localized mode and distributed mode may be fixed,semi-static (constant for tens/hundreds of sub-frames) or even dynamic(different from sub-frame to sub-frame).

In localized mode as well as in distributed mode in—a givensub-frame—one or multiple data blocks (which are inter alia referred toas transport-blocks) may be allocated separately to the same user(mobile station) on different resource blocks, which may or may notbelong to the same service or Automatic Repeat reQuest (ARQ) process.Logically, this can be understood as allocating different users.

L1/L2 Control Signaling

In order to provide sufficient side information to correctly receive ortransmit data in systems employing packet scheduling, so-called L1/L2control signaling (Physical Downlink Control CHannel-PDCCH) needs to betransmitted. Typical operation mechanisms for downlink and uplink datatransmission are discussed below.

Downlink Data Transmission

Along with the downlink packet data transmission, in existingimplementations using a shared downlink channel, such as 3GPP-based HighSpeed Data Packet Access (HSDPA), L1/L2 control signaling is typicallytransmitted on a separate physical (control) channel.

This L1/L2 control signaling typically contains information on thephysical resource(s) on which the downlink data is transmitted (e.g.,subcarriers or subcarrier blocks in case of OFDM, codes in case ofCDMA). This information allows the mobile station (receiver) to identifythe resources on which the data is transmitted. Another parameter in thecontrol signaling is the transport format used for the transmission ofthe downlink data.

Typically, there are several possibilities to indicate the transportformat. For example, the transport block size of the data (payload size,information bits size), the Modulation and Coding Scheme (MCS) level,the Spectral Efficiency, the code rate, etc. may be signaled to indicatethe transport format (TF). This information (usually together with theresource allocation) allows the mobile station (receiver) to identifythe information bit size, the modulation scheme and the code rate inorder to start the demodulation, the de-rate-matching and the decodingprocess. In some cases the modulation scheme maybe signaled explicitly.

In addition, in systems employing Hybrid Automatic Repeat reQuest(HARQ), HARQ information may also form part of the L1/L2 signaling. ThisHARQ information typically indicates the HARQ process number, whichallows the mobile station to identify the Hybrid ARQ process on whichthe data is mapped, the sequence number or new data indicator, allowingthe mobile station to identify if the transmission is a new packet or aretransmitted packet and a redundancy and/or constellation version. Theredundancy version and/or constellation version tells the mobilestation, which Hybrid ARQ redundancy version is used (required forde-rate-matching) and/or which modulation constellation version is used(required for demodulation)

A further parameter in the HARQ information is typically the UE Identity(UE ID) for identifying the mobile station to receive the L1/L2 controlsignaling. In typical implementations this information is used to maskthe CRC of the L1/L2 control signaling in order to prevent other mobilestations to read this information.

The table below (Table 1) illustrates an example of a L1/L2 controlchannel signal structure for downlink scheduling as known from 3GPP TR25.814 (see section 7.1.1.2.3 —FFS=for further study):

TABLE 1 Field Size Comment Cat. 1 ID (UE or group specific) [8-9]Indicates the UE (or (Resource group of UEs) for indication) which thedata transmission is intended Resource assignment FFS Indicates which(virtual) resource units (and layers in case of multi-layertransmission) the UE(s) shall demodulate. Duration of assignment 2-3 Theduration for which the assignment is valid, could also be used tocontrol the TTI or persistent scheduling. Cat. 2 Multi-antenna relatedFFS Content depends on (transport information the MIMO/ format)beamforming schemes selected. Modulation scheme 2 QPSK, 16QAM, 64QAM. Incase of multi-layer transmission, multiple instances may be required.Payload size 6 Interpretation could depend on e.g., modulation schemeand the number of assigned resource units (c.f., HSDPA). In case ofmulti-layer transmission, multiple instances may be required. Cat. 3 IfHybrid 3 Indicates the hybrid (HARQ) asynchronous ARQ ARQ process thehybrid ARQ process current transmission is adopted number is addressing.Redundancy 2 To support version incremental redundancy. New data 1 Tohandle soft buffer indicator clearing. If Retrans- 2 Used to derivesynchronous mission redundancy version hybrid ARQ sequence (to supportis adopted number incremental redundancy) and ‘new data indicator’ (tohandle soft buffer clearing).

Uplink Data Transmission

Similarly, also for uplink transmissions, L1/L2 signaling is provided onthe downlink to the transmitters in order to inform them on theparameters for the uplink transmission. Essentially, the L1/L2 controlchannel signal is partly similar to the one for downlink transmissions.It typically indicates the physical resource(s) on which the UE shouldtransmit the data (e.g., subcarriers or subcarrier blocks in case ofOFDM, codes in case of CDMA) and a transport format the mobile stationshould use for uplink transmission. Further, the L1/L2 controlinformation may also comprise Hybrid ARQ information, indicating theHARQ process number, the sequence number or new data indicator, andfurther the redundancy and/or constellation version. In addition, theremay be a UE Identity (UE ID) comprised in the control signaling.

Variants

There are several different flavors how to exactly transmit theinformation pieces mentioned above. Moreover, the L1/L2 controlinformation may also contain additional information or may omit some ofthe information. For example, the HARQ process number may not be neededin case of using no or a synchronous HARQ protocol. Similarly, theredundancy and/or constellation version may not be needed, if forexample Chase Combining is used (i.e., always the same redundancy and/orconstellation version is transmitted) or if the sequence of redundancyand/or constellation versions is pre-defined.

Another variant may be to additionally include power control informationin the control signaling or MIMO related control information, such as,e.g., pre-coding information. In case of multi-codeword MIMOtransmission transport format and/or HARQ information for multiple codewords may be included.

In case of uplink data transmission, part or all of the informationlisted above may be signaled on uplink, instead of on the downlink. Forexample, the base station may only define the physical resource(s) onwhich a given mobile station shall transmit,. Accordingly, the mobilestation may select and signal the transport format, modulation schemeand/or HARQ parameters on the uplink. Which parts of the L1/L2 controlinformation is signaled on the uplink and which proportion is signaledon the downlink is typically a design issue and depends on the view howmuch control should be carried out by the network and how much autonomyshould be left to the mobile station.

Another, more recent suggestion of a L1/L2 control signaling structurefor uplink and downlink transmission may be found in 3GPP TSG-RAN WG1#50 Tdoc. R1-073870, “Notes from offline discussions on PDCCH contents”,August 2007, available at http://www.3gpp.org and incorporated herein byreference.

As indicated above, L1/L2 control signaling has been defied for systemsthat are already deployed to in different countries, such as forexample, 3GPP HSDPA. For details on 3GPP HSDPA it is therefore referredto 3GPP TS 25.308, “High Speed Downlink Packet Access (HSDPA); Overalldescription; Stage 2”, version 7.4.0, September 2007 (available athttp://www.3gpp.org) and Harri Holma and Antti Toskala, “WCDMA for UMTS,Radio Access For Third Generation Mobile Communications”, Third Edition,John Wiley & Sons, Ltd., 2004, chapters 11.1 to 11.5, for furtherreading.

L1/L2 control signaling reduction techniques

For scheduling (delay-sensitive) services with small data packets, suchas, e.g., VoIP (Voice over IP) or gaming, the downlink L1/L2 controlsignaling can be quite significant if each small data packet needs to besignaled. In a 5 MHz 3GPP LTE system, up to 400 VoIP users can besupported as has been shown in 3GPP TSG-RAN WG1 Meeting #46 Tdoc.R1-062179, “VoIP System Performance for E-UTRA Downlink—AdditionalResults”, (available at

-   http://www.3gpp.org/ftp/tsg_ran/WG1_RL1/TSGR1_46/Docs/). This    results in roughly 10 VoIP packets on the uplink and 10 VoIP packet    on the downlink within a sub-frame, which requires 20 L1/L2 control    channels (10 for uplink data transmission and 10 for downlink data    transmission). Assuming that the payload size of an L1/L2 control    channel carrying an uplink allocation is 35-45 bits and the payload    size of an L1/L2 control channel carrying an downlink allocation is    approximately 35-50 bits, this results in an downlink L1/L2 control    channel overhead of roughly 25-34% (assuming QPSK rate ⅓    transmission of the L1/L2 control channels). This overhead is    significantly larger than for other services (e.g., FTP, HTTP,    audio/video streaming), where the data can be transmitted in large    packets (assumed downlink L1/L2 control channel overhead in this    case is approximately 8-12%). Therefore, within the 3GPP LTE    standardization the several reduction techniques for services with    small data packets are investigated. In the following two    investigated schemes that are discussed by the 3GPP are briefly    explained:

One scheme discussed is based on a grouping of users (e.g., in similarradio conditions) Examples of this scheme are described in the parallelEuropean patent application no. EP 06009854.8, “RESOURCE RESERVATION FORUSERS IN A MOBILE COMMUNICATION SYSTEM” or in 3GPP TSG-RAN-WG2 Meeting#57 Tdoc. R2-070758, “Scheduling for downlink” (available at

-   http://www.3gpp.org/ftp/tsg_ran/WG2RL2/TSGR2_57/Documents/), both    documents being incorporated herein by reference. In this scheme, a    single downlink L1/L2 control channel with a special “group format”    is used. This causes that less “group format” downlink L1/L2 control    channels are required to be transmitted than “normal” L1/L2 control    channels. Although the payload size of the “group format” L1/L2    control channels is larger than that of the “normal” L1/L2 control    channel, a net saving in L1/L2 control signaling overhead is    expected.

Another exemplary scheme is based on the use of a persistent allocationdownlink resources and using with blind detection. Examples of thisscheme are described in the parallel European patent application no. EP06009854.8 mentioned above or in 3GPP TSG-RAN WG2 Meeting #56bisR2-070272, “Signalling optimized DL scheduling for LTE” (available at

-   http://www.3gpp.org/ftp/tsg_ran/WG2_RL2/TSGR2_56bis/Documents/and    incorporated herein by reference). In this exemplary scheme, a    certain set of resource blocks and/or subframes (e.g., a certain    time-frequency window) and possibly a certain set of transport    formats is pre-configured and the UE tries to blindly decode the    possibly transmitted packet on the pre-configured resources with the    pre-configured set of transport formats. For the initial    transmission of a packet the downlink L1/L2 control channel is    omitted, whereas retransmissions are allocated by the downlink L1/L2    control channel. Assuming that the packet error rate for the first    transmission of a packet is considerably low, L1/L2 control    signaling overhead is reduced, e.g., for a 10% packet error rate for    the first transmission, the L1/L2 control signaling overhead can be    roughly reduced by 90%. Typically, in such a scheme, the L1/L2    control signaling transmitted with the retransmission carries    information about the initial transmission (e.g., information about    to a subframe at which the initial transmission took place,    information about the resource block(s) on which the initial    transmission has been allocated and/or information about the    transport format).

It is therefore desirable to reduce of the mobile station (UE)complexity with respect to decoding the downlink L1/L2 control channels.It is further desirable to achieve an additional reduction of thedownlink L1/L2 control signaling overhead and increase in signalingefficiency. Additionally, it may be appreciated by those skilled in theart to implement a simple and less complex downlink L1/L2 controlchannel structure.

SUMMARY OF THE INVENTION

One main aspect of the invention is the definition of at least oneso-called code point in the control channel signals, such as for examplethe L1/L2 control channels as described previously herein. A code pointmay therefore be considered one specific value of a field of the controlchannel signal which is indicating the scheduling mode for an associatedtransmission of user data of a protocol data unit, and further thecontrol channel format. Alternatively, a code point may also be definedas a specific combination of values represented by more than one controlchannel signal field. Likewise, different code points may be defined forthe control channel signal.

One benefit that can be achieved by using code points is the avoidanceof flag fields which indicate the scheduling mode or the format of thecontrol channel. This reduces the size of the control channel and,therefore, the signaling overhead.

According to another aspect of the invention, different scheduling modesmay be used for the transmission of the user data of a service, wherebya code point is used to identify the use of a specific scheduling mode.The different scheduling modes may utilize different formats of thecontrol channel signal so that the code point further indicates aspecific format of the control channel.

Further, the use of different scheduling schemes also increases theflexibility in control channel signaling so that the control channeloverhead may be reduced. For example, there may be two differentscheduling modes defined, wherein one of the scheduling modes onlysignals control channel information for retransmissions of a protocoldata packets (in contrast to providing a control channel signal for eachprotocol data unit transmission—which could be the case for the other,second scheduling mode). This exemplary scheduling mode may for examplebe advantageous for the transmission of user data of delay-sensitiveservices, where the (average) user data size of a protocol data unit issmall in comparison to other service types.

According to one embodiment of the invention, a control channel signalis defined. This control channel signal is suitable for the use in amobile communication system providing at least two different schedulingmodes. The control channel signal comprises at least one controlinformation field consisting of a number of bits, where at least one ofthe values that can be represented by the bits of the at least onecontrol information field defines a code point for indicating thescheduling mode for an associated transmission of user data in for of aprotocol data unit and the control channel format to the receiver. Asindicated above, alternatively, a code point may also be defined by acombination of predetermined values of different control informationfields in the control channel signal. For example, at least the HARQprocess field and the RV field may be used to define the code point.

In one variation the number of bits of the control channel signal isequal for at least two scheduling modes. This may be for exampleadvantageous to simplify the rate matching for the control channels orto reduce the number of different control channel sizes a mobile stationhas to decode.

The at least one control channel field that is used to indicate ascheduling mode by means of the code point may be located at a fixedposition within the control channel signal for all control channelformats. Accordingly, in case the control channel format size is equalfor the different scheduling modes and the control channel field(s) toindicate a code point is/are located at fixed position(s), the detectionof the code point in the control channel signal is simplified for thereceiver of the control channel signal.

Alternatively, in another embodiment of the invention, the controlchannel signal indicates plural code points. These plural code pointsindicate the use of one scheduling mode but different transport formatsof the protocol data unit. Accordingly, not only one specific valuesrepresentable by the bits of a control channel field (or fields) may bedefined as a code point, but different values may be used to indicatedifferent code points. Though there may be plural code points defined,these different code points do not necessarily indicate a correspondingnumber of different scheduling modes. For example, all code pointsdefined for a control channel field may indicate the same schedulingmode, but different control channel information.

In one exemplary embodiment of the invention, the code point isspecified as a specific value of the HARQ process field contained in thecontrol channel signal. For example, one HARQ process may be reservedfor a scheduling mode and the value represented by the bits of the HARQprocess field for indicating the reserved HARQ process defines the codepoint. Accordingly, in this example, the code point indicates thescheduling mode (dependent on which the remaining control channel signalmay be interpreted) and simultaneously specifies the HARQ process of theprotocol data unit.

In another alternative embodiment of the invention the at least onecontrol information field for indicating the code point is a resourceallocation field of the control channel signal. The resource allocationfield may optionally comprise a header and the code point is could bedefined by a specific bit combination of header bits of the resourceallocation field.

In another embodiment, the control information field of the controlchannel signal defining the codepoint is a transport format field of thecontrol channel signal. For example, this transport format field couldindicate plural code points, wherein a subset of the plural code pointsindicates the use of one scheduling mode.

According to a further embodiment of the invention, the controlinformation field defining the codepoint is used to indicate either apersistent scheduling mode or a dynamic scheduling mode.

Another embodiment of the invention relates to a scheduling unit for usein a mobile communication system providing at least two differentscheduling modes. According to this exemplary embodiment, the schedulingunit capable of generating and transmitting a control channel signal asdefined herein.

In a variation of this embodiment, the scheduling unit is furtheradapted to transmit a control channel signal only for retransmissions ofthe protocol data unit, if a first scheduling mode is used for thetransmission of user data.

In an exemplary embodiment, the scheduling unit is adapted to utilizethe first scheduling mode for the transmission of protocol data unitshaving a size below a threshold (e.g., for protocol data units of adelay-critical service, such as VoIP). The second scheduling mode may beused for the transmission of protocol data units having a size above orequal to the threshold (i.e., for example for user data ofdelay-insensitive services).

In another exemplary embodiment, the scheduling unit is adapted toutilize the first scheduling mode for the transmission of protocol datamapped onto a first set of priority queues or logical channels (e.g.,for protocol data units of a delay-critical service, such as VoIP). Thesecond scheduling mode may be used for the transmission of protocol dataunits mapped onto a second set of priority queues or logical channels(i.e., for example for user data of delay-insensitive services).

As indicated above, the control channel format may be different for thedifferent scheduling modes, so that the scheduling unit is capable ofgenerating the different control channel signal formats depending on thescheduling mode used for the transmission of user data.

The scheduling unit according to another embodiment of the inventionuses the HARQ process field of the control signal as the at least onecontrol information field for indicating the code point. In an exemplaryvariation of this embodiment, one HARQ process is reserved for onescheduling mode and the value represented by the bits of the HARQprocess field for indicating the reserved HARQ process defines the codepoint.

Alternatively, according to a further embodiment of the invention, thecontrol information field is a transport format field of the controlchannel signal. In this exemplary embodiment, the transport format fieldmay for example indicate plural code points, and a subset of the pluralcode points could for example indicate the use of one scheduling mode.

In another exemplary embodiment of the invention, the first schedulingmode is a persistent scheduling mode and the second scheduling mode is adynamic scheduling mode.

Another embodiment of the invention is providing a base stationcomprising a scheduling unit according to one of the differentembodiments of the invention described herein.

In one embodiment of the invention, the base station further comprises atransmitter unit for transmitting a control channel signal generated bythe scheduling unit and protocol data units comprising user data to amobile terminal. The base station is further capable of controlling thebase station's transmitter unit to transmit the control channel signalonly for retransmissions of the protocol data unit, in case a firstscheduling mode out of at least two different scheduling modes is usedfor the transmission of the protocol data unit.

The base station according to another embodiment further comprises areceiver unit for receiving a feedback message from the mobile station.The feedback message indicates, whether a protocol data unit previouslytransmitted by the base station has been successfully decoded by themobile station.

In some embodiments of the invention, the first scheduling mode is usedfor the transmission of the user data to the mobile terminal, and afeedback message is received by the receiver unit of the base stationfor an initial transmission of the protocol data unit carrying the userdata. It may be assumed that this feedback message is indicating thatthe protocol data unit has not been decoded successfully by the mobilestation. Accordingly, the base station causes the scheduling unit togenerate a control channel signal for a retransmission of the protocoldata unit. Moreover, the base station may also cause its transmitterunit to retransmit the protocol data unit and the generated controlchannel signal to the mobile station. This control channel signal atleast indicates the transport format and the downlink physical channelresources used for the retransmission and the initial transmission ofthe protocol data unit.

A further embodiment of the invention relates to a mobile station foruse in a mobile communication system and for receiving user data on thedownlink in form of protocol data units. This mobile station comprises areceiver unit for receiving from a base station a subframe of a downlinkphysical channel, and for performing a blind detection on the receivedsubframe to thereby decode an initial transmission of a protocol dataunit conveying user data within the received subframe. The mobilestation further comprises a transmitter unit for transmitting negativefeedback to the base station indicating that the protocol data unit hasnot been decoded successfully during blind detection. In response to thenegative feedback, the receiver unit will receive another subframe ofthe downlink physical channel from the base station comprising a controlchannel signal indicating the transport format and the downlink physicalchannel resources used for the retransmission and initial transmissionof the protocol data unit. Accordingly, the mobile station's decoder isdecoding the protocol data unit based on the control channel signal.

In a further embodiment of the invention, the mobile station comprises a(soft) buffer—such as for example an HARQ buffer—for temporarily storingthe unsuccessfully decoded initial transmission of the protocol dataunit. The decoder soft combines the initial transmission and theretransmission of the protocol data unit prior to decoding.

Another embodiment of the invention provides a computer-readable mediumstoring instructions that, when executed by a processor of a basestation, cause the base station to provide control channel signals in amobile communication system. The base station is caused to providecontrol channel signals in a mobile communication system by generating acontrol channel signal according to one of the different embodimentsdescribed herein, and transmitting the generated control channel signalin a subframe of a physical channel.

A further embodiment of the invention relates to a computer-readablemedium storing instructions that, when executed by a processor of amobile station, cause the mobile station for receive user data on thedownlink in form of protocol data units by receiving from a base stationa subframe of a downlink physical channel, and for performing a blinddetection on the received subframe to thereby decode an initialtransmission of a protocol data unit conveying user data within thereceived subframe, transmitting a negative feedback to the base stationindicating that the protocol data unit has not been decoded successfullyduring blind detection, receiving, in response to the negative feedback,another subframe of the downlink physical channel from the base stationcomprising a control channel signal indicating the transport format andthe downlink physical channel resources used for the retransmission andinitial transmission of the protocol data unit, and decoding theprotocol data unit based on the control channel signal.

The computer-readable medium according embodiment of the invention isfurther storing instructions that, when executed by the processor of themobile station, cause the mobile station to temporarily store theunsuccessfully decoded initial transmission of the protocol data unit abuffer, and to soft combine the initial transmission and theretransmission of the protocol data unit prior to decoding.

BRIEF DESCRIPTION OF THE FIGURES

In the following, the invention is described in more detail in referenceto the attached figures and drawings. Similar or corresponding detailsin the figures are marked with the same reference numerals.

FIG. 1 shows an exemplary data transmission to users in an OFDMA system,

FIG. 2 shows an exemplary data transmission to users in an OFDMA systemin localized mode (LM) having a distributed mapping of L1/L2 controlsignaling,

FIG. 3 shows an exemplary data transmission to users in an OFDMA systemin distributed mode (DM) having a distributed mapping of L1/L2 controlsignaling,

FIG. 4 shows two exemplary L1/L2 control channel signal formats for aspecific scheduling mode (scheduling mode 2), according to oneembodiment of the invention.

FIG. 5 shows an exemplary L1/L2 control channel signal according to oneembodiment of the invention in which a HARQ filed is used to indicate ascheduling mode, and in which the use of the TF/RV/NDI field in thecontrol channel signal is depending on the scheduling mode,

FIG. 6 shows another exemplary L1/L2 control channel signal according toone embodiment of the invention in which a HARQ filed is used toindicate a scheduling mode, and in which the use of the resourceassignment (RA) field and the TF/RV/NDI field in the control channelsignal is depending on the scheduling mode,

FIG. 7 shows an exemplary message exchange between a base station and amobile station according to an embodiment of the invention for datatransmission using scheduling mode 1, and

FIG. 8 shows a mobile communication system according to one embodimentof the invention, in which the message exchange of FIG. 7 may beimplemented, and

FIG. 9 shows a flow chart of an exemplary operation of a base stationaccording to one embodiment of the invention, and

FIG. 10 shows a flow chart of an exemplary operation of a mobile stationaccording to an exemplary embodiment of the invention using schedulingmode 1.

DETAILED DESCRIPTION OF THE INVENTION

The following paragraphs will describe various embodiments of theinvention. For exemplary purposes only, most of the embodiments areoutlined in relation to an (evolved) UMTS communication system accordingto the SAE/LTE discussed in the Technical Background section above. Itshould be noted that the invention may be advantageously used forexample in connection with a mobile communication system such as theSAE/LTE communication system previously described or in connection withmulti-carrier systems such as OFDM-based systems, but the invention isnot limited to its use in this particular exemplary communicationnetwork.

Before discussing the various embodiments of the invention in furtherdetail below, the following paragraphs will give a brief overview on themeaning of several terms frequently used herein and their interrelationand dependencies. Generally, a protocol data unit may be considered adata packet of a specific protocol layer that is used to convey one ormore transport blocks of user data. The user data are typicallyassociated to a service such as for example a VoIP service.

In some embodiments of the invention, the protocol data unit is a MACProtocol Data Unit (MAC PDU), i.e., a protocol data unit of the MAC(Medium Access Control) protocol layer. The MAC PDU conveys dataprovided by the MAC layer to the PHY (Physical) layer. Typically, for asingle user allocation (one L1/L2 control channel—PDCCH—per user), oneMAC PDU is mapped onto one transport block (TB) on Layer 1. A transportblock defines the basic data unit exchanged between Layer 1 and MAC(Layer 2). Typically, the when mapping a MAC PDU onto a transport blockone or multiple CRCs are added. The transport block size is defined asthe size (number of bits) of a transport block. Depending on thedefinition, the transport size may include or exclude the CRC bits.

In general, the transport format defines the modulation and codingscheme (MCS) and/or the transport block size, which is applied for thetransmission of a transport block and is, therefore, required forappropriate (de)modulation and (de)coding. In a 3GPP-based system as forexample discussed in 3GPP TR 25.814, the following relationship betweenthe modulation and coding scheme, the transport block size and theresource allocation size is valid:TBS=CR·M·N_(RE)where N_(RE) is the number of allocated resource elements (RE)—one REbeing identical to one modulation symbol—, CR is the code rate forencoding the transport block, and M is the number of bits mapped ontoone modulation symbol, e.g., M=4 for 16-QAM.

Due to this relationship described above, the L1/L2 control signalingmay only need to indicate either the transport block size or themodulation and coding scheme. In case the modulation and coding schemeshould be signaled, there are several options how to implement thissignaling. For example, separate fields for modulation and coding or ajoint field for signaling both, the modulation and coding parameters maybe foreseen. In case the transport block size should be signaled, thetransport block size is typically not explicitly signaled, but is rathersignaled as a TBS index. The interpretation of the TBS index todetermine the actual transport block size may for example depend on theresource allocation size.

In the following, the transport format field on the L1/L2 controlsignaling is assumed to be indicating either the modulation and codingscheme or the transport block size. It should be noted, that thetransport block size for a given transport block does typically notchange during transmissions. However, even if the transport block sizeis not changed, the modulation and coding scheme may change betweentransmissions, e.g., if the resource allocation size is changed (asapparent for the described relationship above).

The main idea of the invention is the introduction of a so-called codepoint or code points to the control channel signal. A code point is aspecific value representable by a bit combination of one field (out ofplural fields) in the control channel signal format. Alternatively, acode point may be defined as a specific combination of the values ofdifferent control channel signal fields.

A code point (or code points) defined for the control channel signalis/are indicating the use of a specific scheduling mode for thetransmission of the associated user data (in form of protocol dataunits). Depending on the code point, the receiver of the control channelsignal (e.g., the mobile station) recognizes the scheduling mode beingutilized and is capable of interpreting the control channel signalinformation (i.e., the values indicated by the bits of the differentfields in the control channel signal) based on the code point,respectively the scheduling mode indicated by the code point.

In contrast to a (additional) flag (or bit) in the control channelsignaling for indicating the scheduling mode, a code point iscorresponding to (at least) one predetermined value of a (at least one)control channel signal field.

The use of code points avoids additional control signaling overhead (asfor example implied by an additional flag to indicate the schedulingmode). For example, an HARQ field in the control channel signalindicating the HARQ process number used for transmitting the associatedprotocol data unit conveying the user data may have 3 bits which allowssignaling 8 different values, while there may only be 6 HARQ processesavailable. Hence, one of the “remaining” values (or both) may be definedas a code point (or individual code points) to indicate a differentscheduling mode. Alternatively, there may be 8 HARQ processes available(numbered 0 to 7), however, one (or more) of the processes (e.g.,process no. 7=111₂) are configured for transporting VoIP service data.Accordingly, this specific HARQ process number (e.g., process no.7=111₂) can be a code point yielding a specific scheduling mode (andthus optionally a specific control channel signal format). In bothexamples, no additional flag is needed for indicating a secondscheduling mode, which reduces the control signaling overhead.

In one embodiment of the invention, the format of the control channelinformation signal (e.g., the configuration of the control channel interms of its fields, the content of the fields, the size of the fields,and/or the interpretation of the different field values) depends on therespective scheduling mode. For example, it may be assumed that thereare two different scheduling modes available, whereas the schedulingmodes each yield a different control channel signal format. If thescheduler (e.g., located in a base station) sends the control channelsignal yielding the first of the two scheduling modes by means ofsignaling a code point “value”, the receiver of the control channelsignal (for example a mobile station) uses a first reference informationto interpret the control channel information, while the receiver uses asecond reference information to interpret the content of the controlchannel information, if the second scheduling mode is indicated.Irrespective of the scheduling mode, the control channel signal size (interms of the number of bits spent for control channel) is identical. Thescheduling mode is implicitly indicated by the code point not being set(i.e., a value defining no code point is signaled).

In an advantageous embodiment of the invention, the different schedulingmodes are associated with different service types of the user services(user data). For example, a first scheduling mode may be used for thetransmission of user data of services that typically produce onlyprotocol data units for transmission that are relatively small in size(e.g., below a certain threshold) and thus yield a high percentage ofcontrol signaling overhead in conventional systems in comparison to theuser data. One example for such services are delay-sensitive serviceslike VoIP, where only small data packets (or protocol data units) aretransmitted, so that the control channel signaling overhead may besignificant. The second scheduling mode may be for example aconventional scheduling mode and the control channel signaling may bedesigned as described in the Technical Background section.

The generation of small packet protocol data units may have anotherdisadvantage in terms of system throughput. Typically, the number ofcontrol channels is limited (e.g., the control signaling may onlyindicate N different transmissions for a subframe of the physical datachannel). Accordingly, only M transmissions of protocol data units canbe signaled by the control channels per subframe. However, if there aremainly transmissions of services generating small protocol data unitsizes, not all physical radio resources (resource blocks) in a subframeof the physical data channel available for user data transmission may beneeded to transmit M protocol data units, so that system resources arewasted. Accordingly, according to one embodiment of the invention, theuser services that are typically generating protocol data units small insize, like a VoIP service, may be scheduled using one scheduling mode(scheduling mode 1), while other services are scheduled using anotherscheduling mode (scheduling mode 2).

Whether a user service is typically generating protocol data units smallin size may be for example depend on the service class of the service,the type of the service, or may be judged based on the (average)protocol data unit size provided by the service.

As the control channel signal size may be assumed constant in thecommunication system (N bits/control channel)—for example to supportsimple rate matching—there may be no direct improvement to the ratio ofprotocol data unit size to control channel size. However, in thisembodiment, there may be no control channel for initial transmission ofprotocol data units of services generating protocol data units small insize.

Instead, the receiver of the service (e.g., a mobile station) mayreceive a subframe from the physical data channel and tries to decodethe information thereof using blind detection techniques to obtain theprotocol data units. In order to avoid that the mobile station has totry decoding the received subframe information using all possibletransport formats (i.e., all possible modulations and coding schemesavailable in the communication system) there may be a pre-configurationof the transport formats that may be used in connection with thescheduling mode so as to reduce the number of blind detection attemptsto a reasonable number. Alternatively, the transport formats the mobilestation should try for decoding when using blind detection and/or thesubframes which the mobile station should receive and try blind decoding(e.g., every k^(th) subframe) may also be configured (in advance) bycontrol signaling (e.g., in a higher protocol layer).

If blind detection fails, i.e., no protocol data unit can be decodedsuccessfully in a received subframe, the mobile station may store thereceived physical channel information of the subframe (e.g., thereceived soft-values of the received modulation symbols or thelog-likelihood ratios for the demapped modulation symbols) in a buffer(e.g., the HARQ buffer) and sends a negative acknowledgment to thetransmitter. The transmitter may then respond by sending aretransmission for the protocol data unit together with an associatedcontrol channel signal for this retransmission. Accordingly, in thisexemplary embodiment, no control channel signal is sent for the initialtransmission of a protocol data unit, but only for the retransmissionsthereof. As the number of retransmissions may be supposed to besignificantly lower than the number of initial transmissions, thecontrol signaling overhead for the user data transmission may besignificantly reduced in this scheduling mode (scheduling mode 1) foruser data of services that yield small packet sizes, like VoIP services.The other services may be scheduled using another scheduling mode(scheduling mode 2) which may be for example a conventional schedulingmode where all transmissions of user data is accompanied by a respectivecontrol channel signal.

It should be noted that the exact implementation of the blind detectionprocedure is out of the scope of the invention and up to the systemdesign and requirements. In general, blind detection is based on aconcept similar to trial-and-error schemes, where the receivingapparatus receives a physical channel resource (for example a subframe)and tries to decode the received information by trying differentresource allocations and transport formats to demodulate and decode theinformation of the received physical channel resource. In order toreduce the computational requirements of the receiving apparatus, someimplementations only predefine or configure only a given number ofdifferent resource allocations and transport formats for transmissionsthat are received using blind detection. Furthermore, the receivingapparatus may only try to receive specific subframes of a physicalchannel (e.g., every k^(th) subframe) or the subframes to receive and toperform blind detection on may be configured (in advance) by controlsignaling (e.g., in a higher protocol layer), as indicated above.

Next, the operation of the transmitter of the control channel signalaccording to one of the various embodiments described herein and thereceiver thereof will be described in further detail, therebyexemplarily relating to the case of downlink data transmission via a(shared) downlink physical channel. For exemplary purposes a 3GPP LTEnetwork as exemplified in FIG. 8 may be assumed. The mobilecommunication system of FIG. 8 is considered having a “two nodearchitecture” consisting of at least one Access and Core Gateway (ACGW)and Node Bs. The ACGW may handle core network functions, such as routingcalls and data connections to external networks, and it may alsoimplement some RAN functions. Thus, the ACGW may be considered as tocombine functions performed by GGSN and SGSN in today's 3G networks andRAN functions as for example radio resource control (RRC), headercompression, ciphering/integrity protection.

The base stations (also referred to as Node Bs or enhanced Node Bs=eNodeBs) may handle functions as for example segmentation/concatenation ofdata, scheduling and allocation of resources, multiplexing and physicallayer functions, but also RRC functions, such as outer ARQ. Forexemplary purposes only, the eNodeBs are illustrated to control only oneradio cell. Obviously, using beam-forming antennas and/or othertechniques the eNodeBs may also control several radio cells or logicalradio cells.

In this exemplary network architecture, a shared data channel may beused for communication of user data (in form or protocol data units) onuplink and/or downlink on the air interface between mobile stations(UEs) and base stations (eNodeBs). This shared channel may be forexample a Physical Uplink or Downlink Shared CHannel (PUSCH or PDSCH) asknown in 3GPP LTE systems. It is also possible that the shared datachannel and the associated control channels are mapped to the physicallayer resources as shown in FIG. 2 or FIG. 3.

The control channel signals/information may be transmitted on separate(physical) control channels that are mapped into the same subframe towhich the associated user data (protocol data units) are mapped or maybe alternatively sent in a subframe preceding the one containing theassociated information. In one example, the mobile communication systemis a 3GPP LTE system, and the control channel signal is L1/L2 controlchannel information (e.g., information on the Physical Downlink ControlCHannel-PDCCH). Respective L1/L2 control channel information for thedifferent users (or groups of users) may be mapped into a specific partof the shared uplink or downlink channel, as exemplarily shown in FIGS.2 and 3, where the control channel information of the different users ismapped to the first part of a downlink subframe (“control”).

FIG. 7 shows an exemplary message exchange between a base station and amobile station according to an embodiment of the invention for datatransmission using scheduling mode 1. The message exchange may beperformed in the mobile communication network shown in FIG. 8.Accordingly, as the example in FIG. 7 is relating to the downlink datatransmission, the transmitter shown in FIG. 7 may be assumed tocorrespond to base station/Node B NB1 in FIG. 8 and the receiver shownin FIG. 7 may be assumed to correspond to mobile station/UE MS1 in FIG.8. Generally, it may be assumed in FIG. 7 that a retransmissionprotocol, such as Hybrid ARQ, is used between the transmitter (here:base station NB1) and receiver (here: mobile station MS1) of the data(protocol data unit) so as to ensure successful decoding of the data atthe receiver.

In this exemplary 3GPP LTE system according to an embodiment of theinvention a mobile station may simultaneously run services, that aretransmitted using large data packets (e.g., FTP (File TransferProtocol), HTTP (HyperText Transfer Protocol), audio/video streaming)and services that are transmitted using small data packets (e.g., VoIP(Voice over IP), gaming). As mentioned in the technical backgroundsection a reduction in downlink L1/L2 control signaling is desirable forthe services using small data packets. In this exemplary embodiment a1^(st) scheduling mode (scheduling mode 1) is used for the transmissionof protocol data units (PDUs) of services typically having a smallpacket size, while a “normal” 2^(nd) scheduling mode (scheduling mode 2)is employed for other services. Therefore, a mobile station may receivedata transmitted with a 1^(st) or 2^(nd) scheduling mode as definedbelow.

Scheduling mode 1 allows to reduce the L1/L2 control signaling overheadby using a persistent allocation of resources and utilizing blinddetection for the reception, demodulation and decoding of the downlinkdata. Hence, for the initial transmission of a protocol data unit(packet) no L1/L2 control channel is transmitted, but only for firstretransmission of the protocol data unit (and optionally for all orselected ones of further retransmissions).

Scheduling mode 2 may be considered a “normal” or “dynamic” schedulingmode. In this scheduling mode the initial transmission of a packet issignaled via a L1/L2 control channel and retransmissions may or may notbe signaled via a L1/L2 control channel depending on the HARQ operation(e.g., asynchronous or synchronous or adaptive or non-adaptive). Thisscheduling mode may be for example implemented according to thescheduling proposed in the technical background section or as describedin the parallel EP patent application no. EP 07024829.9, entitled“Control Channel Signaling using a Common Signaling Field for TransportFormat and Redundancy Version” of the applicant (filed Dec. 20, 2007,representative's docket number: EP56004), which is incorporated hereinby reference.

Further, it may be assumed for exemplary purposes that for a givensub-frame and given link (uplink or downlink), the mobile station MS1 isallocated either in scheduling mode 1 or in scheduling mode 2. Hence,there is no simultaneous allocation with both modes in a givensub-frame. However, the scheduling mode can change from sub-frame tosub-frame. Also, in a given sub-frame a mobile station may be scheduled.

FIG. 7 exemplifies the user data transmission using scheduling mode 1described above, where it is assumed that the initial transmission isnot signaled by a L1/L2 control signaling. In order to reduce the numberof blind detection attempts, it may be assumed that only a reducednumber of resource assignment and transport format candidates areallowed compared to scheduling mode 2, since the number of blinddecodings and the required soft buffer size are limited. For example, ina 10 MHz system with 50 resource blocks (assuming 11 resource assignmentbits) and 2⁵ transport formats at least 1275×32=40800 candidates forscheduling mode 1 are possible (assuming only consecutive allocations(50 ×(50+1)/2 possibilities) in the RB domain are possible and notconsidering other factors like, e.g., variable control region size). Dueto UE complexity constraints, the number of possible blind decodings persubframe is significantly less than 40800.

Accordingly, the allowed resource assignment and transport formatcandidates may for example be pre-configured or configured 701 by theaccess network using higher layer protocols, such as for example a RadioResource Control (RRC) Protocol or MAC control signaling. Assuming forexemplary purposes 32 resource allocation and transport formatscombinations being (pre-)configured for scheduling mode 1, 32 blinddecodings per subframe are required. In addition, the mobile station maynot know the subframe in which the transmission of the initialtransmission took place. I.e., the blind decoding may need to berequired in several subframes and several subframes may need to bebuffered.

In scheduling mode 1 it is assumed that the L1/L2 control channel of aretransmission carries some information on the resource assignmentand/or the transport format of the initial transmission among possiblyother information. In the above mentioned example, this would require 5bits (log₂(32)) to exactly determine the resource allocation andtransport format, if the subframe number at which the initialtransmission took place is known (less bits could be used in order toreduce the candidates). If the subframe number is not known to themobile station additional information on the subframe number may beincluded to the L1/L2 control channel signal sent with theretransmission.

It should be noted that the increase of subframe candidates for theinitial transmission does not impact the number of blind decodingcomplexity, since this is typically defined by number of blind decodingsper subframe. However, the required buffer size at the receiver isincreased since soft information (bits or modulation symbols) fromadditional subframes of the (shared) downlink physical channel may needto be buffered to allow for soft-combining prior to decoding. In casemultiple subframe candidates for the initial transmission are possible,the L1/L2 control channel of a retransmission may carry some informationof the subframe number being used for the initial transmission in orderto reduce the blind combining complexity.

Returning to FIG. 7, base station NB1 transmits 702 the initialtransmission of a protocol data unit to mobile station MS1 withoutcontrol signaling, i.e., without explicitly indicating the transmissionon the L1/L2 control channel of the subframe for mobile station MS1. Forexample due to a persistent allocation of resources on the (shared)downlink physical channel, mobile station MS1 assumes a usertransmission occurring in the subframe and receives the subframecontaining the initial transmission of the protocol data unit andperforms a blind detection 703 on the information received from thephysical channel by testing the resource allocations and transportformats candidates that have been configures 701 previously.

In the example shown in FIG. 7, it is assumed that the blind detection703 is not successful, i.e., a successful decoding with the testedresource allocation and transport format combinations was not possible(e.g., due to a transmission error in the received information of thephysical channel). Accordingly, mobile station MS1 transmits 704 anegative acknowledgement to base station NB1 to indicate theunsuccessful decoding of the initial transmission. Furthermore, in casethe HARQ protocol supports soft-combining, mobile station MS1 stores thereceived physical channel information (e.g., the soft values of theindividual modulation symbols or the log-likelihood ratios (LLRs) of thechannel bits) for soft-combining with the retransmissions.

Base station NB1 receives the negative acknowledgment (NACK) andgenerates 705 a L1/L2 control channel signal for the retransmission ofthe protocol data unit. The content of the L1/L2 control channel signalwill be discussed in further detail below with respect to FIGS. 5 and 6.Subsequently, base station NB1 transmits 706, 708 the L1/L2 controlchannel signal and the retransmission of the protocol data unit tomobile station MS1.

Mobile station MS1 receives the subframe comprising the L1/L2 controlchannel signal and the retransmission of the protocol data unit andinterprets the content of the control channel signal depending on thescheduling mode indicated in the control channel signal. Using thecontrol channel information comprised in the control channel signal frombase station NB1, mobile station MS1 subsequently tries to decode 709the protocol data unit. Optionally, if soft-combining is provided by theHARQ protocol, the information in the soft buffer of the respective HARQprocess may are combined with the received 708 retransmission of theprotocol data unit prior to decoding 709. If the decoding has beensuccessful, mobile station MS1 sends 710 a positive acknowledgement(ACK) to base station NB1. If decoding of the protocol data unit is notsuccessful, a NACK may be sent and—if soft-combining is utilized—thereceived (shared) downlink physical channel information of theretransmission may also be stored in the associated HARQ soft buffer forlater soft-combining with another retransmission.

The operation of mobile station MS1 and base station NB1 described abovewith respect to FIG. 7 is exemplified in further detail in the flowcharts shown in FIGS. 9 and 10. FIG. 9 shows a flow chart of anexemplary operation of a base station according to one embodiment of theinvention, and FIG. 10 shows a flow chart of an exemplary operation of amobile station according to an exemplary embodiment of the inventionusing scheduling mode 1.

In FIG. 9, upon receiving a new protocol data unit for transmission atthe MAC protocol entity of base station NB1 for transmission to mobilestation MS1, the scheduling unit of base station NB1 first determines901 the scheduling mode that is to be used for the new protocol dataunit.

In case the protocol data unit is to be transmitted using schedulingmode 1, base station NB1 transmits 902 the protocol data unit to mobilestation MS1 (without control signaling) in a similar fashion asdescribed with respect to step 702 of FIG. 7 using a resource allocationand transport format combination that has been for examplepre-configured or configured by a special L1/L2 control channel formator higher layer protocol (see step 701 in FIG. 7).

If the protocol data unit is to be transmitted using scheduling mode 2,base station NB1 selects the appropriate resource allocation andtransport format for the transmission of the protocol and generates 903a L1/L2 control channel signal indicating the selected resourceallocation and transport format for the protocol data unit and notsetting the code point value in the field in order to indicatescheduling mode 2 to mobile station MS1. Next, base station NB1transmits 904 the generated control channel signal and the protocol dataunit to mobile station MS1.

In an exemplary embodiment of the invention, it is assumed that a L1/L2control channel in case of scheduling mode 2 contains at least theinformation depicted in Table 2 and has one of the control channelformats shown in FIG. 4. The upper control channel format in FIG. 4 isindicating the minimum content of the control channel signal accordingto the exemplary definition in Table 2. The second control channelformat at the bottom of FIG. 4 comprises the same control channelinformation as the upper control channel format and optional additionalinformation, such as, e.g., power control for Physical Uplink ControlCHannel (PUCCH,)—e.g., for CQI (Channel Quality Indicator) orACK/NACK—precoding information, transport format information for 2^(nd)codeword, HARQ information for 2^(nd) codeword may be also contained.This additional information may vary in size as indicated by thequestion mark in Table 2.

TABLE 2 Field Bits Comment Resource assignment$\left\lceil {\log_{2}\left( \frac{N_{RB}\left( {N_{RB} + 1} \right)}{2} \right)} \right\rceil$Number of bits depends on the resource allocation scheme and on thesystem bandwidth Number of bits depends on system bandwidth, i.e., onthe number of resource blocks N_(RB) CRC / UE ID 16 MAC UE ID implicitlyencoded in the CRC Transport format /  5 Transport Format: TransportBlock Redundancy version Size or MCS level (New Data Indicator May be aseparate fields or jointly (or Sequence encoded field number)) HybridARQ process  3 number Additional ? E.g., Power control for PUCCH,Information Precoding information, Transport format information for2^(nd) codeword, HARQ information for 2^(nd) codeword

Returning to FIG. 9, irrespective of the scheduling mode, base stationNB1 may receive 905 a feedback for the initial transmission of theprotocol data unit. Accordingly, base station NB1 determines 906 basedon the feedback from mobile station MS1, whether the protocol data unitcould be successfully decoded at mobile station MS1. If so, the nextprotocol data unit may be sent.

If no successful decoding of the protocol data unit is indicated by thefeedback message, base station NB1 selects the appropriate resourceallocation and transport format for the transmission of the protocoldata unit (typically the transport block size is constant for alltransmissions of a protocol data unit) and generates 907 a L1/L2 controlchannel signal indicating the selected resource allocation and transportformat for the protocol data unit and setting an appropriate value inthe field that is used to indicate the scheduling mode to mobile stationMS1. Here, the L1/L2 control channel signal format may depend on theutilized scheduling mode for the protocol data unit.

In case of utilizing scheduling mode 1, the generated L1/L2 controlchannel signal may for example comprise the resource allocation for thealready sent initial transmission (see block 902) and the retransmissionof the protocol data unit to be sent as well as the transport format forthe initial transmission and the retransmission of the protocol dataunit (which should however not change or could be calculated from eachother in typical cases). The indication of the resource allocation andtransport format of the initial transmission in the control channelsignal sent for the retransmission of the protocol data unit may be usedby mobile station MS1 to again try decoding the initial transmission(stored in the HARQ buffer) using the control channel information, butis typically used to properly combine the current retransmission withthe correct content from the HARQ buffer.

In case of utilizing scheduling mode 2 for the protocol data unit thecontrol channel information may have a similar content to thosegenerated and sent in steps 903 and 904. Alternatively, the controlchannel signal may be formed for initial transmissions andretransmissions of a protocol data unit as described in European patentapplication no. EP 07024829.9 mentioned previously herein.

Upon having generated 907 the control channel signal associated to theretransmission of the protocol data unit, the control channel signal andthe retransmission of the protocol data unit is transmitted 908 by basestation NB1.

FIG. 10 shows a flow chart of an exemplary operation of a mobile stationaccording to an exemplary embodiment of the invention using schedulingmode 1. In a first step, mobile station MS1 receives 1001 a subframefrom the (shared) downlink physical channel. For example due to apersistent allocation or reservation of resources on the (shared)downlink physical channel, mobile station MS1 is aware of a potentialuser transmission occurring in the subframe and performs a blinddetection 1002 on the information received from the physical channel bytesting the resource allocations and transport formats candidates thathave for example been configured previously.

In case the blind detection is successful, i.e., the protocol data unitcould be successfully decoded by mobile station MS1, mobile station MS1transmits 1004 a positive acknowledgement (ACK) to base station NB1. Ifblind detection 1002 is not successful, i.e., no matching resourceallocation and transport format is found (e.g., due to a transmissionerror in the received information of the physical channel), mobilestation MS1 transmits 1005 a negative acknowledgement to base stationNB1 to indicate the unsuccessful decoding of the initial transmission.Optionally, in case the HARQ protocol supports soft-combining, mobilestation MS1 stores 1006 the received physical channel information (e.g.,the soft values of the individual modulation symbols or thelog-likelihood ratios (LLRs) of the channel bits) for soft-combiningwith the retransmissions in the HARQ buffer region associated to theprotocol data unit's HARQ process.

After having sent a negative acknowledgement, mobile station MS1 furtherreceives another subframe 1007 of the (shared) downlink physicalchannel. This subframe comprises a L1/L2 control channel signal that isindicating control channel information for the initial transmission andthe retransmission of the protocol data packets, as for exampledescribed with respect to FIGS. 5 and 6 below. Upon successfullyobtaining 1008 the control channel signal, mobile station MS1 mayperform 1009 a soft-combining of the buffered physical channelinformation of the initial transmission and the physical channelinformation of the retransmission contained in the subframe received instep 1007 prior to decoding the protocol data unit. If it is determined1010 by mobile station MS1 that the protocol data unit could besuccessfully decoded, mobile station MS1 transmits 1011 a positiveacknowledgement to base station NB1. Otherwise it transmits 1012 anegative acknowledgement and stores the physical channel information ofthe retransmission contained in the subframe received in step 1007 inthe HARQ buffer region of the process used for transmitting the protocoldata unit.

As indicated previously herein, a code point may be defined in the HARQprocess field of the control channel signal. In this example, thecontrol channel signal is assumed to have a control channel field forsignaling the HARQ process number of the protocol data unit.

FIG. 5 shows an exemplary L1/L2 control channel signal according to oneembodiment of the invention in which a HARQ filed is used to indicate ascheduling mode, and in which the use of the TF/RV/NDI field in thecontrol channel signal is depending on the scheduling mode.

For scheduling mode 2, the TF/RV/NDI field is indicating the transportformat (TF), the redundancy version (RV) and the new data indicator(NDI). These parameters of the control channel may be for examplejointly encoded as exemplarily illustrated in FIG. 5 and as described inEuropean patent application no. EP 07024829.9. Alternatively, theseparameters of the protocol data unit may also be encoded separately inindividual fields, or only the transport format and the redundancyversion of the protocol data unit may be jointly encoded as alsodescribed in European patent application no. EP 07024829.9.

In order to allow for a reasonable soft buffer management, for datatransmitted with scheduling mode 1 it may be beneficial to reserve acertain HARQ process out of the existing processes. In this case, apreconfigured process (“code point”), e.g., 111, may be used to indicatethat the L1/L2 control channel has the format of scheduling mode 1.

In one exemplary embodiment, the resource assignment field is unchangedfor scheduling mode 1 and 2, since this allows for having fullflexibility for the resource allocation of the retransmission. Also theCRC/UE ID field (comprising the CRC checksum masked with the identifierof the mobile station or group of mobile stations to which the controlchannel information is destined) is not changed in the control channelsignal format for scheduling mode 1 and scheduling mode 2, since it maybe required to identify the targeted mobile station(s) and to preventother mobile stations from reading the content of the given controlchannel.

In the example shown in FIG. 5, the content/interpretation of theTF/RV/NDI field(s) is (are) is depending on the scheduling mode. Usingscheduling mode 1 for the transmission of the protocol data unit, thecontrol channel signal comprises a resource assignment (RA) fieldindicating the resource block(s) of the subframe carrying the protocoldata unit (note that the resource assignment may have changed betweeninitial and retransmission). In this example, the resource allocationfield has the same size as in the control channel format for schedulingmode 2. As the transport block size of the retransmission may be assumedidentical to same for the initial transmission this information may beencoded and obtained from the subsequent control channel field providinginformation on the initial transmission.

Further, the control channel signal comprises the before mentioned fieldproviding information on the initial transmission (which iscorresponding to the TF/RV/NDI field of the format for scheduling mode 2in its position in the control channel signal and the field size). Thisfield may for example be used to indicate the transport format(transport block size) and redundancy version of the initialtransmission. For scheduling mode 1 no NDI is required, as the controlchannel signal is only sent for retransmissions. Therefore, incomparison to the format for scheduling mode 2, the entire field can beused for control information on the initial transmission. The controlinformation on the transport format and the redundancy version may bejointly encoded in the control channel field providing information onthe initial transmission. Alternatively, the control channel fieldproviding information on the initial transmission may be divided intoseparate sub-fields for the transport format and the redundancy version.Alternatively, the control channel field providing information on theinitial transmission may only contain the transport format and aredundancy version may not be required.

For scheduling mode 1, the code point “111” is set in the HARQ processfield to indicate on the one hand the HARQ process number of theprotocol data unit and on the other hand scheduling mode 1 being usedfor the transmission of the protocol data unit.

For scheduling mode 2, the HARQ process field indicates the appropriateHARQ process number and thus implicitly indicates scheduling mode 2being used for the transmission of the protocol data unit and thecorresponding control channel format.

In an alternative embodiment of the invention, the size and position ofsome fields (except for the field(s) defining the code point(s)) in thecontrol channel format may differ for the different scheduling modes.This is exemplified in FIG. 6 showing another exemplary L1/L2 controlchannel signal according to one embodiment of the invention in which aHARQ filed is used to indicate a scheduling mode, and in which the useof the resource assignment (RA) field and the TF/RV/NDI field in thecontrol channel signal is depending on the scheduling mode. Essentially,the formats of the control channel for scheduling modes 1 and 2 in termsof the fields contained in the control channel signal corresponds to theexamples shown in FIG. 5. However, the size of the resource assignmentfield is changed for scheduling mode 1 in comparison to the format ofscheduling mode 2. The same is true for size and use of the TF/RV/NDIfield(s) in the scheduling mode 2 control channel format.

In the example shown in FIG. 6, the resource assignment field forscheduling mode 1 is smaller than the corresponding field for schedulingmode 2. This design is based on the assumption that for scheduling mode1 not all possible resource assignments (as for scheduling mode 2) areneeded to the retransmission of scheduling mode 1, since e.g., onlyrelatively small allocations are used for scheduling mode 1 or since areduced number of different allocations with the same allocation sizeare sufficient. Accordingly, more control information bits may beassigned to the field indicating the control channel information for theinitial transmission of the protocol data unit.

In another embodiment, another field than the HARQ process field of thecontrol channel signal is used to define a code point. For example, thecontrol channel signal may comprise a separate field indicating thetransport format of the protocol data unit (TF field). According to thisembodiment, a single value representable by the bits of the TF field isreserved as a code point to indicate the use of scheduling mode 1 forthe transmission of the protocol data unit. Further, in a variation ofthis embodiment, the RV/NDI field may be used in the control channelsignal to jointly encode the redundancy version and the new dataindicator for the protocol data unit.

In another embodiment multiple TF “code points” may be reserved, asexemplarily shown in Table 3 below. Assuming that the number of requiredtransport formats (e.g., Transport Block Sizes or MCS levels) forscheduling mode 1 is limited, this allows for determining the TBS or MCSlevel from the (pre-)configured candidates with a relatively small lossof TF values for scheduling mode 2. For example, if the TF field has 6bits and 8 TBS values are preconfigured for scheduling mode 2, only 8out of 64 TF values are “lost” for scheduling mode 1. In addition, thesignaling of one of these “code points” could indicate the change ofusage of all or part of the remaining control channel fields asdescribed above.

TABLE 3 Signaled Signaled Value Value TF (binary) (decimal) (TBS) Ranges0000 0 50 Scheduling 0001 1 100 mode 2 0010 2 150 0011 3 230 0100 4 3000101 5 . . . 0110 6 . . . 0111 7 500 1000 8 . . . 1001 9 . . . 1010 10 .. . 1011 11 . . . 1100 12 1000 1101 13 Pre-config. TBS 1 Scheduling 111014 Pre-config. TBS 2 mode 1 1111 15 Pre-config. TBS 3

Also in case the transport format is jointly encoded with the redundancyversion of the protocol data unit as described in European patentapplication no. EP 07024829.9 a code point may be defines in the jointfield as shown in Table 4. In a similar fashion as exemplified in Table4, also multiple code points could be defined.

TABLE 4 Signaled Signaled Value Value TF Scheduling (binary) (decimal)(TBS) RV Ranges mode 0000 0 . . . 0 TF range Scheduling 0001 1 . . . 0mode 2 0010 2 . . . 0 0011 3 . . . 0 0100 4 . . . 0 0101 5 100 0 0110 6120 0 0111 7 150 0 1000 8 200 0 1001 9 . . . 0 1010 10 . . . 0 1011 11 .. . 0 1100 12 N/A 0 RV range 1101 13 1 1110 14 2 1111 15 Pre-config. 0Code Scheduling TBS 1 point mode 1

As a further alternative embodiment of the invention, the resourceassignment field of the control channel signal could be used fordefining one or more code points in a similar fashion as describedabove. In a variation of this embodiment, the resource assignment fieldhas a header as specified in 3GPP RAN WG1 Meeting #51 Tdoc.R1-074582,“Downlink Resource Allocation Mapping for E-UTRA”, available athttp://www.3gpp.org and incorporated herein by reference, and a specificbit combination(s) of the header bits in the resource allocation fieldmay be defined as a code point(s).

Similarly, in a further embodiment the L1/L2 control channel signalcomprises a separate RV field for indicating the redundancy version andthe RV field is used to define at least one code point.

In a further alternative embodiment of the invention, the controlchannel (in scheduling mode 2) may have a field carrying power controlcommands for the associated downlink data transmission (on the PDSCH),for the PUCCH or for some other channel. To indicate scheduling mode 1 acode point of this field may be used, since for scheduling mode 1 thisfield is less important or not required.

In addition to the different approaches for defining code points in asingle field of the control channel signal, individual code points maybe defined in respective fields could be reserved to indicate schedulingmode 1. In an exemplary embodiment of the invention, a combination ofthe values of the resource assignment field and the TF field may defineone or more code points. In this exemplary embodiment, the resourceassignment and transport format candidates of the blind detection (inthe first transmission) can be reduced, e.g., the “code points” in thein the TF field are used to indicate the preconfigured TBSs as shown inTable 3 and a similar scheme for reducing the resource allocationcandidates can be used in the resource allocation field. In addition,the signaling of these “code points” could indicate the change of theusage of part of the remaining control channel fields as describedabove.

Examples of mobile communication systems in which the principles of theinvention outlined herein may be utilized are communication systemsutilizing an OFDM scheme, a MC-CDMA scheme or an OFDM scheme with pulseshaping (OFDM/OQAM).

Furthermore, it should also be noted that though most embodiments of theinvention have been described with respect to subframes of a (shared)downlink physical channel which comprise the user data transmission andthe associated control channel signal for the user data transmission,also other designs are possible in which control channel information ofa user data transmission is sent in an earlier subframe of the (shared)downlink physical channel than that containing the user datatransmission, or where there is a separate physical control channel forthe signaling of the control channel information.

Furthermore, the (shared) downlink physical channel mentioned herein maybe for example a Downlink Shared CHannel (PDSCH) of a 3GPP LTE system.

Another embodiment of the invention relates to the implementation of theabove described various embodiments using hardware and software. It isrecognized that the various embodiments of the invention may beimplemented or performed using computing devices (processors). Acomputing device or processor may for example be general purposeprocessors, digital signal processors (DSP), application specificintegrated circuits (ASIC), field programmable gate arrays (FPGA) orother programmable logic devices, etc. The various embodiments of theinvention may also be performed or embodied by a combination of thesedevices.

Further, the various embodiments of the invention may also beimplemented by means of software modules, which are executed by aprocessor or directly in hardware. Also a combination of softwaremodules and a hardware implementation may be possible. The softwaremodules may be stored on any kind of computer readable storage media,for example RAM, EPROM, EEPROM, flash memory, registers, hard disks,CD-ROM, DVD, etc.

Furthermore, it should be noted that the terms mobile terminal andmobile station are used as synonyms herein. A user equipment may beconsidered one example for a mobile station and refers to a mobileterminal for use in 3GPP-based networks, such as LTE.

In the previous paragraphs various embodiments of the invention andvariations thereof have been described. It would be appreciated by aperson skilled in the art that numerous variations and/or modificationsmay be made to the present invention as shown in the specificembodiments without departing from the spirit or scope of the inventionas broadly described.

It should be further noted that most of the embodiments have beenoutlined in relation to a 3GPP-based communication system and theterminology used in the previous sections mainly relates to the 3GPPterminology. However, the terminology and the description of the variousembodiments with respect to 3GPP-based architectures is not intended tolimit the principles and ideas of the inventions to such systems.

Also the detailed explanations given in the Technical Background sectionabove are intended to better understand the mostly 3GPP specificexemplary embodiments described herein and should not be understood aslimiting the invention to the described specific implementations ofprocesses and functions in the mobile communication network.Nevertheless, the improvements proposed herein may be readily applied inthe architectures described in the Technical Background section.Furthermore, the concept of the invention may be also readily used inthe LTE RAN currently discussed by the 3GPP.

The invention claimed is:
 1. A user equipment (UE), comprising:reception circuitry which, in operation, receives, from a base stationthat provides a dynamic scheduling mode and a persistent schedulingmode, a control channel signal that includes at least a HARQ (HybridAutomatic Repeat request) process field; and control circuitry coupledto the reception circuitry and which, in operation, select thepersistent scheduling mode to communicate with the base station, when avalue in the HARQ process field and a value in another predeterminedfield in the received control channel signal at least partiallyconstitute a predetermined combination of values, and interpret at leastone of control information format fields other than the fields used forselecting the persistent scheduling mode in the control channel signaldifferently between the dynamic scheduling mode and the persistentscheduling mode, based on the predetermined combination of values. 2.The UE according to claim 1, wherein the number of bits of the controlchannel signal is equal for the dynamic and persistent scheduling modes.3. The UE according to claim 1, wherein the number of resourceallocation variations is less in the persistent scheduling mode than inthe dynamic scheduling mode.
 4. The UE according to claim 1, wherein theHARQ process field is located at a fixed position within the controlchannel signal for all control information formats.
 5. The UE accordingto claim 1, wherein the value in the HARQ process field is a valuerepresented by at least a portion of bits in the HARQ process field. 6.The UE according to claim 1, wherein the another predetermined field isan RV (redundancy version) field.
 7. A method implemented by a userequipment (UE), the method comprising: receiving a control channelsignal from a base station that provides a dynamic scheduling mode and apersistent scheduling mode, the control channel signal including atleast a HARQ (Hybrid Automatic Repeat request) process field, selectingthe persistent scheduling mode to communicate with the base station,when a value in the HARQ process field and a value in anotherpredetermined field in the received control channel signal at leastpartially constitute a predetermined combination of values, andinterpreting at least one of control information format fields otherthan the fields used for selecting the persistent scheduling mode in thecontrol channel signal differently between the dynamic scheduling modeand the persistent scheduling mode, based on the predeterminedcombination of values.
 8. The method according to claim 7, wherein thenumber of bits of the control channel signal is equal for the dynamicand persistent scheduling modes.
 9. The method according to claim 7,wherein the number of resource allocation variations is less in thepersistent scheduling mode than in the dynamic scheduling mode.
 10. Themethod according to claim 7, wherein the HARQ process field is locatedat a fixed position within the control channel signal in all controlinformation formats.
 11. The method according to claim 7, wherein thevalue in the HARQ process field is a value represented by at least aportion of bits in the HARQ process field.
 12. The method according toclaim 7, wherein the another predetermined field is an RV (redundancyversion) field.